The 911 GT3 (996) with the older style headlights were not officially sold in the US. Of course I've seen them for track use but I am sure a few were driven around on the roads, which was not allowed. And people may think they have seen GT3's running around, but the regular Carrera was available with the GT3 look (rims, GT3 spoiler and side skirts).

But the revised GT3, with the newer turbo headlights and different wing is officially sold here in the US. Thats why you can see those occasionally.